A Comparison of a Mono-, Twin-, and Double-Scroll Turbine for Automotive Applications

Abstract

As a means of meeting ever increasing emissions and fuel economy demands, car manufacturers are using aggressive engine downsizing. To maintain the power output of the engine, turbocharging is typically used. Due to the mismatch of the mass flow characteristics of the engine to the turbocharger, at low engine mass flow rates (MFRs), the turbocharger can suffer from slow response known as “Turbolag.” Mono-scroll turbines are capable of providing good performance at high MFRs and in conjunction with low inertia mixed flow turbines can offer some benefits for transient engine response. With a multi-entry system, the individual volute sizing can be matched to the single mass flow pulse from the engine cylinders. The exhaust pulse energy can be better utilized by the turbocharger turbine improving turbocharger response, while the interaction of the engine exhaust pulses can be better avoided, improving the scavenging of the engine. The behavior of a mono-scroll turbocharger with the engine using engine simulation tools has been well established. What requires further investigation is the comparison with multi-entry turbines. Computational fluid dynamics (CFD) has been used to examine the single-admission behavior of a twin- and double-scroll turbine. Turbocharger gas stand maps of the multi-entry turbines have been measured at full and single admissions. This data have been used in a 0D engine model. In addition, the turbine stage has been tested on the engine, and a validation of the engine model against the engine test data is presented. Using the validated engine model, a comparison has been made to understand the differences in the sizing requirements of the turbine and the interaction of the mono-scroll and multi-entry turbines with the engine. The impact of the different efficiency and MFR trends of the mono and multi-entry turbochargers is discussed, and the tradeoffs between the design configurations regarding on-engine behavior are investigated.